The Transdisciplinary Methods Core interrelates with other cores and the overall theme of the CDAAR by: (1) building and strengthening links between disciplines and specialties to produce research products of outstanding vigor and novelty, and (2) providing CDAAR investigators with the necessary and appropriate quantitative and qualitative methods and instruments to achieve transdisciplinary research objectives. The methodologic contributions of this core will include techniques for studying risk behaviors in natural habitats, methodologies for economic analyses of drug abuse and HIV/AIDS, strategies for community-based interventions, maintenance of contact with study participants, and appropriate uses of structured instrumentation and assessment, immunologic assessment, virologic assessment, and genetic studies. To achieve these goals, this core will address the following specific aims: (1) Integrate laboratory science with clinical, economic, and behavior research, (2) Facilitate access, recruitment, and follow-up of human populations for drug abuse and HIV/AIDS research, (3) Provide CDAAR investigators with the tools and expertise to select and apply appropriate measures and instruments in a variety of research settings, including high quality standardized immunological, neuroendocrine, virological, and molecular assays, (4) Provide investigators with a repertoire of qualitative techniques to enhance investigations of the values and beliefs that underlie behavior. (5) Make available to investigators techniques with which they can conduct economic analyses of the human behavior that they are studying, (6) Assist CDAAR investigators in the development of protocols for protection of human subjects and to provide expertise and training in issues related to human subjects related and ethics, and (7) To develop training programs to assist CDAAR researchers with the development of novel approaches to the integration of molecular biology with areas related to outreach, recruitment, assessment, data collection, client retention and follow-up.